The present invention relates generally to an induction furnace for melting or casting reactive metals or alloys such as uranium metal or uranium alloys, and more particularly to an induction furnace constructed of carbon-free materials so as to inhibit the contamination of the melted metal or alloy with carbon impurities.
Induction heated furnaces have been used extensively for melting and casting reactive metals such as uranium and uranium alloys. These induction furnaces commonly utilize graphite crucibles and graphite induction rings which are coated with protective oxide surfaces. Considerable problems are encountered in using induction furnaces in which these carbon bearing materials are utilized for the construction of the furnace in that moisture is absorbed by the induction rings, crucibles and the oxide coatings at ambient conditions during downtime of the furnace. The carbon and/or carbon oxides are in turn released from the moisturized graphite materials and the oxide coatings into the furnace environment during the melting of the reactive metals. As a result of this carbon, accurate control of the alloy compositions is considerably hampered since the carbon in the furnace environment reacts with the metal or alloy melt to contaminate the melt with carbon so as to considerably alter the physical properties of the metal or alloy. Other problems associated with known induction furnaces is in the use of zirconia thermal insulation since zirconia at certain levels of densities is a susceptor of the magnetic flux in the induction furnace which caused considerable susceptor arcing with the induction coil and often resulted in damaging the induction coil and disrupting the furnace operation.
Efforts to decrease the carbon contamination of melts in induction furnaces include the coating of the graphite crucibles with various oxides such as yttria and the like. However, even with such essentially impermeable coatings sufficient carbon is still derived from the crucibles and graphite susceptor rings so as to excessively contaminate the melt with carbon.